Polyphenylene ether resin, also known as polyphenylene oxide, is recognized in the art as an engineering plastic having excellent high heat distortion temperature, high stiffness and high strength at elevated temperatures. However, it has the drawbacks of poor impact strength, poor processibility due to high melt and glass transition temperatures and poor chemical resistance thereby limiting its field of application.
In an attempt to overcome these drawbacks, polyphenylene ether resin has been blended with other resins. For example, U.S. Pat. No. 3,383,435 discloses a composition comprising polyphenylene ether resin and a polystyrene or a rubber-modified styrene resin, wherein the rubber component is a highly unsaturated rubber, such as, polybutadiene. U.S. Pat. No. 3,658,945 and 3,943,191 disclose compositions comprising polyphenylene ether resin and an EPDM-modified styrene resin. In these patents the EPDM rubber replaces the highly unsaturated rubber used in the U.S. Pat. No. 3,383,435 in an attempt to increase the impact strength. However, no significant improvement was achieved.
Other compositions have been disclosed comprising a polyphenylene ether resin and an EPDM-modified styrene resin with additional components. U.S. Pat. No. 4,172,826 discloses compositions comprising polyphenylene ether resin, EPDM-modified styrene resin, hydrogenated A-B-A block copolymers and, optionally, a filler. In U.S. Pat. No. 4,483,958 the composition disclosed comprises polyphenylene ether resin, EPDM-modified styrene resin, an inorganic filler and a thermoplastic elastomer selected from styrene-conjugated diolefin copolymers and styrene polymer grafted polyolefin.
Various blend compositions of polyolefins and polyphenylene ether resins have been made in an attempt to improve properties, such as impact strength, chemical resistance and melt processibility of polyphenylene ether resins. For example, U.S. Pat. No. 3,361,851 to Gowan discloses a composition comprising polyphenylene ether resin and polypropylene, wherein a small quantity of polypropylene is dispersed in the polyphenylene ether resin. The reference teaches that the amount of the polypropylene that can be incorporated is limited to no more than 10% by weight of the total composition and that incorporating amounts of polypropylene exceeding 10% results in phase separation during the molding of such compositions and delamination of the molded articles.
It has also been disclosed that larger amounts of polypropylene can be incorporated in polyphenylene ether resin compositions if elastomeric block copolymers are present and, optionally, polystyrene. Compositions of this kind are described in U.S. Pat. No. 4,166,055; 4,764,559 and 4,383,082 and EPA 263678. These patents teach improved compatibility between the polyolefin and polyphenylene ether and improved impact strength. However, there is a substantial decrease in flexural modulus and heat distortion temperature.
U.S. Pat. No. 4,713,416 to Del Giudice et al. discloses a composition of (a) polyphenylene ether resin, (b) a thermoplastic copolymer other than polystyrene that is incompatible with polyphenylene ether resins, such as crystalline olefin polymers, polycarbonates, aromatic polyesters and polyamides, and (c) a compatibility promoting agent. When the incompatible thermoplastic copolymer is a crystalline olefin polymer the reference teaches using either (a) block copolymers consisting of a vinyl aromatic monomer and a crystalline olefin or (b) the product obtained by grafting a vinyl aromatic monomer onto a crystalline polymer of a C.sub.2 -C.sub.6 olefin.